Fixed network resistor

ABSTRACT

A fixed resistor network has an insulating substrate, a plurality of film resistors arranged on a top surface of the insulating substrate, terminal electrodes formed for the film resistors on each lengthwise sidewall of the insulating substrate at a given pitch along the sidewall, and recesses provided between the terminal electrodes. The occurrence of solder bridges between the terminal electrodes during solder mounting and the occurrence of chipping in the terminal-electrode-forming areas between the recesses on the lengthwise sidewall are both reduced by making the width of the recesses along the lengthwise sidewall either 0.44 to 0.48 times or 0.525 to 0.625 times the pitch.

TECHNICAL FIELD

The present invention relates to a surface-mount fixed network resistorhaving a single insulating substrate of rectangular shape on a topsurface of which are arranged at least three film resistors, and on alengthwise side of which are formed terminal electrodes for solderconnection for each of the resistor films.

BACKGROUND ART

In a prior-art fixed resistor network of this type having, for example,four film resistors such as that shown in FIGS. 12 to 14, an insulatingsubstrate 1′ with a rectangular shape of length L and width W as seen inplan view has four film resistors 2′ arranged on a top surface of thesubstrate 1′ in the lengthwise direction thereof and has, for both endsof each film resistor 2′, terminal electrodes 4′ which are formed onboth lengthwise sidewalls 3′ of the insulating substrate 1′. The fixedresistor network is surface mounted on a printed board by soldering eachof the terminal electrodes 4′.

In addition, the prior art provides recesses 5′ in areas between theterminal electrodes 4′ on both lengthwise sidewalls 3′ of the insulatingsubstrate 1′. When individual terminal electrodes 4′ are formed on bothlengthwise sidewalls 3′, the individual recesses 5′ reliably separatethese individual terminal electrodes 4′ from each other (see, forexample, Japanese Examined Patent Publication No. S6-18123). A covercoat 7′ made of a material such as glass is formed on the top surface ofthe insulating substrate 1′ so as to cover each of the film resistors2′.

Fixed resistor networks having the above construction must satisfy thefollowing conditions.

(a) When the fixed resistor network is mounted on a printed board bysoldering, of the individual terminal electrodes 4′ for both ends of theindividual film resistors 2′, the occurrence of solder bridging betweenneighboring terminal electrodes 4′ must be low.

(b) When individual terminal electrodes 4′ are formed on both lengthwisesidewalls 3′ of the insulating substrate 1′ by the application anddrying or firing of a conductive paste, connection of the conductivepaste within a recess 5′ between neighboring terminal electrodes 4′ mustbe infrequent.

(c) The occurrence of the chipping or breaking off of material interminal-electrode-forming areas 6′ between recesses 5′ on thelengthwise sidewalls 3′ of insulating substrate 1′ must be low.

(d) The frequency of cracking of the insulating substrate 1′ at therecesses 5′ must be low.

To address these requirements, prior-art fixed resistor networks have aconstruction in which, letting the pitch of the terminal electrodes 4′along the lengthwise sidewalls 3′ of the insulating substrate 1′ be P,the width A′ at areas 6′ where the terminal electrodes 4′ are formed(referred to below as “terminal-electrode-forming areas”) between therecesses 5′ on the lengthwise sidewalls 3′ has been set to A′=approx.0.6×P; the width B′ along the lengthwise direction 3′ of insulatingsubstrate 1′ at the recesses 5′has been set to B′=approx. 0.4×P, and thedepth C′ at each recess 5′ from the lengthwise direction 3′ has been setapproximately equal to the width A′ at the terminal-electrode-formingareas 6′.

This type of construction has led to the following sorts of problems.

That is, in fixed resistor networks of a size where the pitch P betweenthe terminal electrodes 4′ has been set to 0.5 mm, the width B′ of therecesses 5′ becomes 0.4×0.5=approx. 0.2 mm, which is small. When thesefixed network chip resistors are surface mounted by soldering onto aprinted board or the like, there is a strong possibility that solderbridging will occur so as to connect, of the above individual terminalelectrodes 4′, neighboring terminal electrodes 4′ separated by a recess5′.

In fixed resistor networks of a size where the pitch P between theterminal electrodes 4′ has been set to 0.4 mm, the width B′ of therecesses 5′ becomes B′=0.4×0.4=approx. 0.16 mm, which is even smaller.During solder mounting, the occurrence of solder bridges betweenneighboring terminal electrodes 4′ in such cases becomes very high.

Moreover, in fixed resistor networks of a size where the pitch P hasbeen set to 0.4 mm, the depth C′ at each recess 5′ is C′=0.24 mm. At aresistor size having a pitch P of 0.4 mm, the width W of the insulatingsubstrate 1′ is 0.6 mm, and so the depth C′ to width W ratio for theinsulating substrate 1′ becomes large, resulting in frequent cracking ofthe insulating substrate 1′ at these recesses 5′. Furthermore, as thedepth C′ at the recesses 5′ increases, the projecting length at theterminal-electrode-forming areas 6′ positioned between these recesses 5′increases, resulting in more frequent chipping or breaking off ofmaterial in these terminal-electrode-forming areas 6′.

On the other hand, as the depth C′ at the recesses 5′ decreases, whenthe terminal electrodes 4′ are formed by applying a conductive paste tothe terminal-electrode-forming areas 6′ situated between the recesses5′, the conductive paste often extends into the recess 5′ from bothsides and connects therein.

It is an object of the invention to provide a fixed resistor networkwhich overcomes these problems.

DISCLOSURE OF THE INVENTION

In a first aspect, the invention provides a fixed resistor networkhaving an insulating substrate of rectangular shape in plan view, atleast three film resistors formed on a top surface of the insulatingsubstrate at a suitable pitch in a lengthwise direction of theinsulating substrate, terminal electrodes formed for the film resistorson a lengthwise sidewall of the insulating substrate, and recessesprovided between the terminal electrodes, a pitch between the terminalelectrodes along the sidewall being at least 0.5 mm, wherein each recesshas a width along the lengthwise sidewall which is from 0.44 to 0.48times the pitch of the terminal electrodes, andterminal-electrode-forming areas between the recesses have a width alongthe lengthwise sidewall which is from 0.56 to 0.52 times the pitch ofthe terminal electrodes.

During the soldering of fixed resistor networks, to eliminate solderbridging between neighboring terminal electrodes across an interveningrecess, the width of the recess between the terminal electrodes shouldbe made larger than the width of the terminal-electrode-forming areas ofthe insulating substrate.

However, making the width of the recesses larger than the width of theterminal-electrode-forming areas without increasing the pitch of theterminal electrodes means that the width of theterminal-electrode-forming areas will be smaller, reducing the strengthof these areas and leading to a higher occurrence of defects such as thechipping or breaking off of material.

We therefore studied the relationship between the width of theterminal-electrode-forming areas and the width of the recesses when thepitch between the terminal electrodes is held constant, whereupon wefound that it is desirable to set the width of the recesses at 0.44 to0.48 times the pitch of the terminal electrodes and to set the width ofthe terminal-electrode-forming areas between the recesses at 0.56 to0.52 times the pitch.

That is, by having the width of the terminal-electrode-forming areasbetween the recesses and the width of the recesses satisfy the aboveconditions, the chipping or breaking off of material at theterminal-electrode-forming areas can be reliably prevented withoutincreasing the pitch of the film resistors, and thus without making theinsulating substrate larger. At the same time, during soldering, solderbridging between neighboring terminal electrodes across an interveningrecess can be greatly reduced.

In a second aspect, the invention provides a fixed resistor networkhaving an insulating substrate of rectangular shape in plan view, atleast three film resistors formed on a top surface of the insulatingsubstrate at a suitable pitch in a lengthwise direction of theinsulating substrate, terminal electrodes formed for the film resistorson a lengthwise sidewall of the insulating substrate, and recessesprovided between the terminal electrodes, a pitch between the terminalelectrodes along the sidewall being not more than 0.4 mm; wherein eachrecess has a width along the lengthwise sidewall of the insulatingsubstrate which is from 0.525 to 0.625 times the pitch of the terminalelectrodes, and terminal-electrode-forming areas between the recesseshave a width along the lengthwise sidewall of the insulating substratewhich is from 0.475 to 0.375 times the pitch of the terminal electrodes.

In this arrangement, when the pitch between the terminal electrodes is0.4 mm, the width of the recesses along the lengthwise sidewalls of theinsulating substrate becomes 0.21 to 0.25 mm, and the width of theterminal-electrode-forming areas between the recesses along thelengthwise sidewalls of the insulating substrate becomes 0.19 to 0.15mm. As illustrated in detail below in the following embodiments, thishas the effect of making it possible to satisfy at the same timeconditions (a), (b) and (c) required of fixed resistor networks.

Moreover, in this second aspect of the invention, as noted above, inaddition to making the width of the recesses along the lengthwisesidewall of the insulating substrate from 0.525 to 0.625 times the pitchof the terminal electrodes and making the width of theterminal-electrode-forming areas between the recesses along thelengthwise sidewall of the insulating substrate from 0.475 to 0.375times the pitch of the terminal electrodes, by also setting the depth ofthe recesses from the lengthwise sidewall of the insulating substrate tofrom 0.512 to 0.645 times the width of the terminal-electrode-formingareas, the depth of the recesses from the lengthwise sidewall of theinsulating substrate becomes 0.077 to 0.12 mm. This has the effect of,in addition to above conditions (a), (b) and (c), also satisfying at thesame time above condition (d).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of the invention;

FIG. 2 is a plan view of the same embodiment;

FIG. 3 is an enlarged cross-sectional view taken along III—III in FIG.2;

FIG. 4 is a perspective view showing the insulating substrate used inthe first embodiment;

FIG. 5 is a perspective view of a second embodiment of the invention;

FIG. 6 is a perspective view showing the insulating substrate used inthe second embodiment;

FIG. 7 is a perspective view of a third embodiment of the invention;

FIG. 8 is a perspective view showing the insulating substrate used in afourth embodiment of the invention;

FIG. 9 is a plan view showing a fifth embodiment of the invention;

FIG. 10 is an enlarged cross-sectional view taken along X—X in FIG. 9;

FIG. 11 is a perspective view showing the insulating substrate used thefifth embodiment;

FIG. 12 is a perspective view showing a fixed resistor network accordingto the prior art;

FIG. 13 is a plan view of the same prior-art fixed resistor network; and

FIG. 14 is a perspective view showing the insulating substrate used inthe same prior-art fixed resistor network.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention are described below in conjunction with theattached diagrams.

FIGS. 1 to 4 show a first embodiment of the invention.

In these diagrams, the symbol 1 represents a ceramic insulatingsubstrate having, in a plan view, a rectangular shape with a length L of2.0 mm and a width W of 1.0 mm. This insulating substrate 1 has formed,on a top surface thereof, four film resistors 2 which are arranged inthe lengthwise direction of the insulating substrate 1.

Terminal electrodes 4 which are electrically connected to both ends ofeach film resistor 2 are formed on both longitudinal sidewalls 3 of theinsulating substrate 1 at a pitch P=0.5 mm along the longitudinalsidewalls 3. Recesses 5 are provided in areas between the individualterminal electrodes 4 on both of the lengthwise sidewalls 3 of theinsulating substrate 1.

Each terminal electrode 4 is formed so as to extend to a bottom surfaceof the insulating substrate 1. On the top surface of the insulatingsubstrate 1, a cover coat 7 made of a material such as glass is formedso as to cover each film resistor 2.

Each recess 5 has a width B along the lengthwise sidewall 3 such thatB=0.46×P=0.23 mm. Between these recesses 5 are areas 6 where theterminal electrodes 4 are formed, i.e., terminal-electrode-forming areas6, each of which has a width A along the lengthwise sidewall 3 such thatA=0.54×P=0.27 mm.

In experiments we carried out, compared with the prior art, the abovearrangement was able to greatly reduce the occurrence of defects such asthe chipping or breaking off of material at theterminal-electrode-forming areas 6. At the same time, during mounting ofthe fixed resistor network onto a printed board or the like bysoldering, compared with the prior art, the above arrangement was ableto greatly reduce the occurrence of solder bridging between, of theabove terminal electrodes 4, those neighboring terminal electrodes 4separated by a recess 5.

We also found from experiments that it is desirable to set the width Bof the recesses 5 to B=(0.48 to 0.44)×P and to set the width A of theterminal-electrode-forming areas 6 to A=(0.52 to 0.56)×P.

That is, when the terminal-electrode-forming areas 6 had a width Agreater than 0.56×P=0.28 mm and the recesses 5 had a width B less than0.44×P=0.22 mm, the frequency of solder bridging between neighboringterminal electrodes 4 separated by a recess 5 increased. When theterminal-electrode-forming areas 6 had a width A less than 0.52×P=0.26mm and the recesses 5 had a width B greater than 0.48×P=0.24 mm, thefrequency of defects such as the chipping or breaking off of material atthe terminal-electrode-forming areas 6 increased.

Next, FIGS. 5 and 6 show a second embodiment of the invention.

This second embodiment is a three-element fixed resistor networkcomposed of a single insulating substrate 11, of rectangular shape in aplan view, on which three film resistors 12 are arranged. Terminalelectrodes 14 for both ends of the individual film resistors 12 areformed on both lengthwise sidewalls 13 of the insulating substrate 11 ata pitch P=0.5 mm along the lengthwise sidewalls 3, and recesses 15 areprovided between the terminal electrodes 14. In addition, a cover coat17 is formed on a top surface of the insulating substrate 11.

In this embodiment as well, by setting the terminal-electrode-formingareas 16 between the recesses 15 to a width A along the lengthwisesidewalls 13 such that A=(0.52 to 0.56)×P and setting the recesses 15 toa width B along the lengthwise sidewalls 13 such that B=(0.48 to0.44)×P, defects such as the chipping or breaking off of material in theterminal-electrode-forming areas 16 can be reliably reduced. At the sametime, during mounting of the fixed resistor network onto a printed boardor the like by soldering, the occurrence of solder bridging betweenneighboring electrodes 14 separated by a recess 15 can be reliablyreduced.

FIG. 7 shows a third embodiment of the invention.

This third embodiment is a fixed resistor network in which the pitch Pbetween the terminal electrodes has been set at 0.5 mm. In this device,on one lengthwise sidewall 23 of the lengthwise sidewalls 23 and 23′ ofan insulating substrate 21, terminal electrodes 24 are formed to theabove pitch P=0.5 mm at one end of each of four film resistors 22arranged on a top surface of the insulating substrate 21, and recesses25 are provided between these individual terminal electrodes 24. On theother lengthwise sidewall 23′ of the lengthwise sidewalls 23 and 23′ ofthe insulating substrate 21, at least one common terminal electrode 24′which is electrically connected through a conductor pattern 28 to theother end of the four film resistors 22 is separately formed. Moreover,a cover coat 27 is formed on the top surface of the insulating substrate21.

In this arrangement, as in the first embodiment described above, bygiving the terminal-electrode-forming areas 26 between the recesses 25on one lengthwise sidewall 23 of the insulating substrate 21 a widthA=(0.52 to 0.56)×P and by giving the recesses 25 a width B=(0.48 to0.44)×P, as noted above, defects such as the chipping or breaking off ofmaterial at the terminal-electrode-forming areas 26 can be reliablyreduced and, during mounting of the fixed resistor network onto aprinted board or the like by soldering, the occurrence of solderbridging between neighboring terminal electrodes 24 separated by arecess 25 can be reliably reduced.

Moreover, in this third embodiment, dummy terminal electrodes 24″ andrecesses 25′ therebetween are provided on the other lengthwise sidewall23′ of the insulating substrate 21, in the same manner as the individualterminal electrodes 24 and recesses 25 on the first lengthwise sidewall13.

Obviously, this invention is not limited to three-or four-element fixedresistor networks having three or four film resistors on one insulatingsubstrate as in the foregoing embodiments, and may also be applied tomulti-element fixed network resistance having five or more filmresistors.

FIG. 8 shows a fourth embodiment of the invention.

This fourth embodiment is a multi-element fixed resistor network havingan insulating substrate 31 with a length L of 3.8 mm and a width W of1.6 mm. Terminal-electrode-forming areas 36 for the formation ofterminal electrodes at both ends of each film resistor 32 formed on atop surface of the insulating substrate 31 are provided at a pitch P=0.5mm along lengthwise sidewalls 33 of the insulating substrate 31.Recesses 35 are provided between these terminal-electrode-forming areas36.

In this embodiment too, as described above, by giving theterminal-electrode-forming areas 36 between recesses 35 provided on thelengthwise sidewalls 33 of the insulating substrate 31 a width A=(0.52to 0.56)×P and by giving the recesses 35 a width B=(0.48 to 0.44)×P,defects such as the chipping or breaking off of material at theterminal-electrode-forming areas 36 can be reliably reduced and, duringmounting of the fixed resistor network onto a printed board or the likeby soldering, the occurrence of solder bridging between neighboringterminal electrodes separated by a recess 35 can be reliably reduced.

FIGS. 9 to 11 show a fifth embodiment of the invention.

This embodiment is a four-element fixed resistor network in which thepitch P between the terminal electrodes was set at 0.4 mm.

In these diagrams, the symbol 41 represents a ceramic insulatingsubstrate having, in a plan view, a rectangular shape with a length L of1.39 mm and a width W of 0.6 mm. This insulating substrate 41 hasformed, on a top surface thereof, four film resistors 42 so as to bearranged in the lengthwise direction of the insulating substrate 41.

Terminal electrodes 44 that are electrically connected to both ends ofthe film resistors 42 are formed, on lengthwise sidewalls 43 at bothedges of the insulating substrate 41, at a pitch P=0.4 mm along thelengthwise direction of the insulating substrate 41.

Recesses 45 having a width B along the lengthwise sidewall 43 and asuitable depth C from the lengthwise sidewall 43 are provided in areasbetween the terminal electrodes 44 on the lengthwise sidewalls 43 of theinsulating substrate 41. In other words, terminal-electrode-formingareas 46 having a width A along the lengthwise sidewall 43 are providedin areas between the recesses 45 on both lengthwise sidewalls 43, with aportion of the terminal electrodes 44 being formed at these terminalelectrode-formed areas 46.

Each of the terminal electrodes 44 extends to a bottom surface of theinsulating substrate 41. Moreover, a cover coat 47 made of a materialsuch as glass is formed on the top surface of the insulating substrate41 so as to entirely cover all the film resistors 42.

On both the lengthwise sidewalls 43 of the insulating substrate 41, thewidth A of the terminal-electrode-forming areas 46 between the recesses45 is set at A=P×(0.475 to 0.375) such as to make A=0.19 to 0.15 mm, andthe width B of the recesses 45 is set at B=P×(0.525 to 0.625) such as tomake B=0.21 to 0.25 mm.

Moreover, the depth C of each recess 45 from the lengthwise sidewall 43is set at 0.512 to 0.645 times the width A of theterminal-electrode-forming areas 46, i.e., C=A×(0.512 to 0.645), such asto make C=0.077 to 0.12 mm.

In experiments, we found that during mounting of the fixed resistornetwork onto a printed board or the like with solder, the frequency ofsolder bridging between neighboring terminal electrodes 44 separated bya recess 45 from among the terminal electrodes 44 changes markedly at arecess 45 width W of 0.20 mm. That is, by giving each recess 45 a widthB of 0.20 mm or more, the frequency of solder bridging can be reduced toabout one-tenth or less the frequency when the width B is less than 0.20mm.

We have also found from experiments that when terminal electrodes 44 areformed at the terminal-electrode-forming areas 46 by applying aconductive paste, connection of the conductive paste within the recess45 between the electrodes changes markedly at a recess 45 depth C ofapproximately 0.077 mm. That is, by setting the depth to 0.077 mm ormore, the frequency of such conductive paste connections across recesses45 can be reduced to about one-tenth or less the frequency when thedepth C is less than 0.077 mm.

Based on these results and assuming the above dimensions to havesomewhat of a margin of safety, we concluded that the width B of therecesses 45 is set to preferably at least 0.21 mm, i.e., B=P×0.525 ormore, and the depth C of the recesses 45 is set to preferably at least0.077 mm, i.e., C=A×0.512 or more.

Yet, although the occurrence of solder bridging between the terminalelectrodes 44 can be reduced by making the width B of the recesses 45larger, increasing this width B decreases the width A of theterminal-electrode-forming areas 46. Moreover, although the occurrenceof conductive paste connections between terminal electrodes 44 can bereduced by increasing the depth C of the recesses 45, increasing thedepth C increases the length of the terminal-electrode-forming areas 46.This gives the terminal-electrode-forming areas 46 a narrower shape,resulting in more frequent chipping or breaking off of material at theterminal-electrode-forming areas 46. Moreover, increasing the depth C ofthe recesses 45 results in a higher frequency of cracking in the area ofthe recesses 45 on both lengthwise edges of the insulating substrate 41.

We thus carried out experiments on the relationship between the width Aof the terminal-electrode-forming areas 46 and the width C of therecesses 45.

The results showed that, by setting the width A of theterminal-electrode-forming areas 46 to at least 0.15 mm, i.e., A=P×0.375or more, and setting the depth C of the recesses 45 to not more than0.12 mm, i.e., C=A×0.645 or less, it is possible to greatly reduce boththe frequency of the chipping or breaking off of material at theterminal-electrode-forming areas 46 and the frequency of cracking in thearea of the recesses 45 of the insulating substrate 41.

1. A fixed resistor network comprising an insulating substrate ofrectangular shape in plan view, at least three film resistors formed ona top surface of the insulating substrate at a suitable pitch in alengthwise direction of the insulating substrate, terminal electrodesformed for the film resistors on a lengthwise sidewall of the insulatingsubstrate, and recesses provided between the terminal electrodes, apitch between the terminal electrodes along the sidewall being at least0.5 mm; wherein each recess has a width along the lengthwise sidewallwhich is from 0.44 to 0.48 times the pitch of the terminal electrodes,and terminal-electrode-forming areas between the recesses have a widthalong the lengthwise sidewall which is from 0.56 to 0.52 times the pitchof the terminal electrodes.
 2. The fixed resistor network according toclaim 1, wherein the terminal electrodes, recesses andterminal-electrode-forming areas are provided on both lengthwisesidewalls of the insulating substrate.
 3. The fixed resistor networkaccording to claim 1, wherein the terminal electrodes, recesses andterminal-electrode-forming areas are provided on at least one of the twolengthwise sidewalls of the insulating substrate.
 4. The fixed resistornetwork according to any one of claims 1 to 3, wherein the pitch betweenthe terminal electrodes is 0.5 mm or approximately 0.5 mm.
 5. The fixedresistor network according to any one of claims 1 to 3, wherein theinsulating substrate has a length L of approximately 2.0 mm and a widthW of approximately 1.0 mm.
 6. The fixed resistor network according toany one of claims 1 to 3, wherein the insulating substrate has a lengthL of approximately 3.8 mm and a width W of approximately 1.6 mm.
 7. Afixed resistor network comprising an insulating substrate of rectangularshape in plan view, at least three film resistors formed on a topsurface of the insulating substrate at a suitable pitch in a lengthwisedirection of the insulating substrate, terminal electrodes formed forthe film resistors on a lengthwise sidewall of the insulating substrate,and recesses provided between the terminal electrodes, a pitch betweenthe terminal electrodes along the sidewall being not more than 0.4 mm;wherein each recess has a width along the lengthwise sidewall of theinsulating substrate which is from 0.525 to 0.625 times the pitch of theterminal electrodes, and terminal-electrode-forming areas between therecesses have a width along the lengthwise sidewall of the insulatingsubstrate which is from 0.475 to 0.375 times the pitch of the terminalelectrodes.
 8. The fixed resistor network according to claim 7, whereinthe recesses have a depth from the lengthwise sidewall of the insulatingsubstrate which is from 0.512 to 0.645 times the width of theterminal-electrode-forming areas.
 9. The fixed resistor networkaccording to claim 7, wherein the recesses have a width along thelengthwise sidewall of the insulating substrate of 0.21 to 0.25 mm andthe terminal-electrode-forming areas between the recesses have a widthalong the lengthwise sidewall of the insulating substrate of 0.19 to0.15 mm.
 10. The fixed resistor network according to claim 8, whereinthe recesses have a depth of 0.077 to 0.12 mm from the lengthwisesidewall of the insulating substrate.